The invention relates to folding apparatus and more particularly to a signature or map folding apparatus for producing at least one cross-grain fold in individual signatures on a continuous web.
In the printing arts, the term "signature" refers generally to any printed sheet of material to be folded. The sheet of material may be cut from a continuously printed web of successive individual such sheets or "signatures" and thereafter folded to the desired configuration. In the case of books, the individual sheets or signatures are folded to comprise individual pages of the book which must be interfitted with other folded signatures in a given order to produce the completed book.
In the following description, the invention will be illustrated with reference to the problem of producing cross-grain folds in a previously plow-folded signature, such as a map. In this regard, a plurality of such maps may be printed, usually on both sides of a substantially continuous web of paper material.
Thereafter, the web is fed to a so-called plow folding apparatus to produce plow folds, which comprise an accordian-like series of oppositely directed folds therein. The plow-folded web must thereafter be cut into individual maps or signatures and cross-grain folded to produce individual maps or "books" as they are sometimes called. Generally speaking, two such cross-grain folds are effected in each signature, map, or book at spaced apart locations.
In accordance with a preferred embodiment of the invention, the folding apparatus also effects the separation or cutting of the printed, plow-folded web into individual signatures, maps or books. Additionally, it is also desirable to count out the books into groups of a given number for packaging, such that each group or package contains 25 books or maps, for example. In accordance with a further preferred form of the invention, this counting and sorting or delivery into such groups of a given number is also carried out in conjunction with the folding apparatus.
Producing two folds in a previously plow-folded web and simultaneously separating the web into individual signatures has been attempted in the prior art. Prior art practice has included carrying out the steps at a number of work stations, involving a number of transfers of the work, time-consuming and expensive manual procedures.
It should be recognized in this regard that the cutting and cross-grain folding of individual signatures such as a previously plow-folded map presents a difficult problem when run "on-line" at "full press speeds". By "on-line", it is meant that the foregoing process of printing, plow-folding and thereafter cutting and cross-grain folding takes place in a continuous fashion, with the web being fed through a plurality of machines or apparatus adapted to perform each operation. By "full press speed", is meant the relatively high speed operation of an automated printing press which may be on the order of several feet per second of web therethrough.
One problem noted in prior art attempts to produce such cross-grain folds on line and at full press speed is the problem of maintaining the first fold effected in the signature while producing the second fold. In this regard, it will be appreciated that both ends of the map are to be folded generally inwardly with respect to the central portion of the map or signature, and hence, a problem arises in effecting the two folds so that the folded segment or portion of the map or signature overlies the shorter folded segment thereof. One prior art apparatus attempted to proceed by producing the shorter or "rear" fold initially and thereafter feeding the map or signature to a second folding station for producing the front or longer fold. In this regard, the terms "short" and "long" with respect to the folds refer to the length of map or signature remaining from the fold itself to the distal or free (when cut) end of the signature. The terms "front" and "rear" with respect to the folds refer to the direction of travel of the map or signature as it is initially introduced into the apparatus.
However, this prior art method resulted in a relatively great length of unsupported signature protruding initially from the apparatus while the first fold was being effected. Such a length of unsupported signature tended to produce a twisting or sideways turning moment upon the signature, in turn causing the first cross-grain fold to be out of line, that is, not exactly at right angles to the longitudinal axis of signature.
A further problem in the prior art apparatus occurred in the attempt to maintain control over the once-folded signature while effecting the second fold therein. Apparatus proposed heretofore attempted transfer of the signature between individual drums or cylinders, each of which carried a folding apparatus in the form of a pair of jaws thereon for effecting a given fold. However, this attempted transfer proved difficult to carry out accurately and often resulted in undue stretching or tensioning of the map or signature as it was passed from one drum or cylinder to the next.
A related problem is that referred to as tucker blade "wipe-out". In this regard, each of the above-mentioned folding jaws cooperated with a generally flat, protruding blade member mounted to an opposing drum or cylinder and known as a "tucker blade". The function of the tucker blade is to urge the proper portion of the map or signature into the cooperating jaw to effect the fold at the proper location thereon. However, this blade inevitably frictionally contacts or "wipes" against the surface of the signature or map to either side of the center line of the intended folds, as it proceeds into and out of engagement with this center line or relative narrow portion across the map where the fold is to be effected. This is due primarily to the opposite directions of rotation of the respective cylinders upon which the tucker blade and jaws are respectively carried.